(i) Technical Field
The present invention relates to a surface-emitting semiconductor laser, a surface-emitting semiconductor laser device, an optical transmission device, and an information processing device.
(ii) Related Art
Surface-emitting semiconductor lasers, which are capable of emitting a laser beam in a direction perpendicular to the substrate and readily formed in an array by two-dimensional integration, can be used as, for example, a light source for optical communications, a light source for electronic equipment, or a recording unit of an electrophotographic system.
Common surface-emitting semiconductor lasers include a pair of distributed Bragg reflectors (DBRs) formed on a semiconductor substrate, an active layer interposed between the pair of DBRs, and a cavity spacer layer. When a current is injected into the active layer through electrodes disposed on the respective DBRs, lasing occurs in a direction perpendicular to the substrate.
Limiting a rise in the temperature of the active layer enhances the reliability and temperature characteristics of the surface-emitting semiconductor laser. One effective way to limit the temperature rise is to use a material having high thermal conductivity such as AlAs, which has the highest thermal conductivity among AlxGa1-xAs, as a material constituting the DBRs. In general, an oxide confinement layer is formed in the vicinity of the active layer in order to achieve a low-current operation. In order to form the oxide confinement layer, a mesa structure having an adequate size is formed by etching, and thereby a cross section of the oxide confinement layer, which is composed of an easily oxidizable material such as AlAs, is exposed. In general, the bottom of the etched portion is positioned within the lower DBR located away from the active region because, if the bottom of the etched portion is located in the vicinity of the active layer, the reliability of the surface-emitting semiconductor laser may be degraded. In the case where the bottom of the etched portion is present within the lower DBR, a portion of the lower DBR is exposed to an oxidizing atmosphere. Therefore, it is impossible to use AlAs, which is easily oxidizable material, as a material constituting the DBRs. Thus, in an oxide confinement surface-emitting semiconductor laser, it is difficult to limit a rise in the temperature of the active layer since it is not possible to use AlAs as a material of the lower DBR.